INTRODUCTION. 



The primary object of this Memoir is to throw light on the structural aspect of the major 

 abnormalities occurring in fishes, particularly in the trout and salmon. Nearly half of the text, 

 and practically all the illustrations, are devoted to this purpose. The Plate-figures consist of 

 photomicrographs of sections and other specimens, and of reconstruction diagrams which, like the 

 anatomical descriptions in the text, are based on the study of numerous series of sections. I 

 have to express equal indebtedness and thanks to the Trustees of the Carnegie Bequest for the 

 support which has made possible the publication of the work in its present form. 



The greater part of my trout material was obtained some years ago from a Hatchery at 

 Lochwinnoch, through the good offices of Mr. John Peden who was then in charge. Specimens 

 were also received from the Loch Lomond Hatchery and from various private sources. In addition 

 I had the privilege of examining at leisure the Salmonid material in the collection of the Eoyal 

 College of Surgeons of England. 



I desire to acknowledge indebtedness to the kindness and skill of my friend, the late Thomas 

 Pieid, M.D., LL.D., for greatly-valued assistance in the preparation of a number of the photographs. 

 My best thanks are also due to Mr. J. G. Connell, F.R.M.S., for help in compiling the Indexes, 

 of which there are three, namely, one of Structures and Subjects, one of Fishes, and one of Authors. 

 The first includes full references to the various Plates and Figures in which individual structures 

 receive illustration. It is through the courtesy of the Council of the Zoological Society of 

 London that illustrations from papers of mine which appeared in their Proceedings, 1903, Vol. II., 

 and 1906, Vol. I., have been reproduced in Plates XVII.-XX. and XXV, and this courtesy is 

 herewith gratefully acknowledged. 



Whilst, as stated above, the main content of the work is structural, occasion has also been 

 taken to deal briefly with other aspects of major monstrosity in fishes, and to point out relationships 

 with higher vertebrates. 



In addition, the minor abnormalities form a large and varied group, many sections of which 

 might well receive separate and lengthy discussion. My aim has been to describe these as 

 briefly as is consistent with moderate adequacy of treatment, and to make it easy for future 

 workers to get into touch with the chief present sources of information in each subject. It 

 is hoped that this latter object has been attained through the literature-references and the 

 Bibliography. 



The study of monstrosities among fishes merits a distinct and important place in the biological 

 field. Although this study has come latest in point of time, its data are now in process of 

 incorporation with those of general vertebrate teratology, the foundations of which they have 

 not failed to deepen and extend. The following circumstances favour this result : (1) In the 

 bony fishes, which provide by far the greatest number of monstrosities, the ova are abundant 

 and the processes of fertilisation and development take place outside the body of the parent. 

 Plentiful material is available at all stages for observation and experiment. Facts of the greatest 

 value have thereby been ascertained, particularly with reference to mode of origin and early 

 development. (2) Although the major types of monstrosity in fishes do not survive the period 

 of nutrition by the yolk sac, still at the end of this stage the cartilaginous skeleton and practically 

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